The present invention relates to a method and apparatus for generating multiple pitch tones in multiplexed organs, and more particularly to generate the frequencies which simulate the tone of a chime.
If it is known that to simulate the sound produced by a chime, a predetermined combination of pitches are sounded in flute voices and with a certain amount of sustain. For a C note, the notes E, C, G, C and F, in that order, are played.
To key these notes employing prior art techniques would require a bank of keyers for each of the notes in addition to the note played. Because this is very costly in terms of hardware, many organs in the past have deleted one or more of the notes in the chime, thereby reducing the number of additional keyers necessary. In the case of a C chime, the E and F notes would be deleted. Although this created a chime-like sound, it fell short of producing a sound truly simulative of a chime. The chime generators would use either resistors or multiple contact key switches to sum together the frequencies to be keyed.
In multiplexed organs, one prior art technique for sounding a plurality of tones or voices for the depression of a single key is to pass the serial data stream through a shift register and then connect selected stages of the shift register to an output line. This results in a plurality of additional keydown pulses appearing in time slots subsequent to the initial keydown pulse and it is well suited for voicing. The difficulty encountered when using this technique for chime generation, however, is that the tones necessary for a true chime lie on both sides of the note played so that simple delaying and reinsertion of the initial keydown pulse will not produce a keydown pulse in the time slot ahead of the note-played pulse in the data stream. Although the keydown pulse could be shifted through a long shift register so as to appear in the data stream for the next scan of the keyboard, a shift register of this length is impractical for reasons of cost.